The present invention relates to a method for detecting decompression of tires and a device thereof, and a program for judging decompression of tires. More particularly, the present invention relates to a method for detecting decompression of tires which can detect decompression of tires even if the traveling and stoppage of a vehicle are repeated for a short time and a device thereof, and a program for judging decompression of tires.
A detection device of decompression of tires has conventionally used a principle that since the outer diameter of a tire (the dynamic load radius of a tire) is reduced more than that of a tire having a normal inner pressure when the pressure of a tire is reduced, wheel speed (rotational angular velocity) is increased as compared with other normal tires. For example, a method of detecting the lowering of an inner pressure from the relative difference of the wheel speeds of a tire uses as a judgment value;DEL={(V1+V4)/2−(V2+V3)/2}/{(V1+V2+V3+V4)/4}×100 (%)(For example, refer to Japanese Unexamined Patent Publication No. 305011/1988).
Wherein V1 to V4 are the wheel speeds of a front left tire, a front right tire, a rear left tire and a rear right tire, respectively.
By the way, a judgment value being the above-mentioned relative comparison value of tire property which is determined from the relative difference of the wheel speeds of tires varies a little depending on the various traveling conditions of a vehicle.
Accordingly, in a conventional detection device of decompression of tires, an average value obtained by moving average of the relative comparison value (judgment value) obtained by the measurement for a fixed time, for example, for continuous six seconds and the like is used, and decompression of tires is designed to be detected by a result whether its average value exceeds a fixed threshold or not.
However, when the above-mentioned average value is used, the judgment value is calculated, for example, by every one second, the moving average value for 6 seconds of the judgment value is determined and its average value is compared with a threshold. However, a chance for calculating the judgment value for at least continuous 6 seconds must be obtained in order to calculate the moving average value for 6 seconds, and if the judgment value exceeding the threshold is not obtained for 6 seconds, the moving average value does not exceeds the threshold.
When traveling which is terminated for less than 6 seconds after actuation is repeated in like manner as, for example, cars are on a traffic jammed highway, there is no chance for calculating the moving average value even if the judgment value exceeds the threshold; therefore there is a problem that decompression of tires cannot be detected nevertheless the pressures of tires are reduced.